Various techniques have been proposed to provide broadcast services within a cellular network. For example, multimedia broadcast multicast service (MBMS) is a broadcast service that has been proposed for implementation within Global System for Mobile Communications (GSM) and Universal Mobile Telecommunications System (UMTS) cellular networks. MBMS is split into a bearer service and a user service. The bearer service includes a multicast mode and a broadcast mode, and the user service offers a streaming delivery method and a download delivery method. The streaming delivery method can be used for a continuous transmission, such as mobile television (TV) services, and the download method is intended for download-and-play services. With reference to FIG. 1, a diagram 100 illustrates proposed channel allocations and frame formats for a third generation partnership project (3GPP) cellular network implementing an enhanced MBMS. As is depicted, the cellular network implements a cellular downlink channel 102, operating at a center frequency f1, and a downlink channel 104, operating a center frequency f2.
The downlink channel 102 is divided into high-speed shared control channel (HS-SCCH) timeslots to provide cellular services to subscriber stations. The downlink channel 104 is divided into high-speed physical downlink shared channel (HS-PDSCH) and MBMS timeslots to provide MBMS in conjunction with high-speed downlink packet access (HSDPA). An enhanced MBMS cellular network also implements a cellular uplink channel 106 operating at a center frequency f3. The uplink channel 106 is divided into dedicated physical channel (DPCH) timeslots. While the MBMS timeslots are interleaved with HS-PDSCH timeslots on the downlink channel 104, information delivery on the downlink channel 102 has not been coordinated with information delivery on the downlink channel 104.
Recently, the Institute of Electrical and Electronics Engineers (IEEE) promulgated a standard (i.e., IEEE 802.16) for local and metropolitan area networks. More specifically, IEEE 802.16e describes requirements for an air interface for fixed and mobile broadband wireless access systems. The Worldwide Interoperability for Microwave Access (WiMAX) forum was formed to promote conformance and interoperability of the IEEE 802.16 standard. In general, technology that conforms to the IEEE 802.16 standard facilitates delivery of last mile wireless broadband access, as an alternative to cable and digital subscriber line (DSL) services. IEEE 802.16 defines a multicast and broadcasting service (MBS) that is implemented in a single frequency network (SFN) configuration, as opposed to a multi-frequency network configuration. As is known, a typical cellular network has employed a number of different channels (frequency bands) to reduce interference between neighboring cells of the cellular network and has reused frequency bands in non-adjacent cells.
IEEE 802.16e, which is based on orthogonal frequency division multiple access (OFDMA), defines a partial use of subcarrier (PUSC) operation mode in which a channel is divided into orthogonal segments each with non-overlapping subcarrier permutations and a full use of subcarrier (FUSC) operation mode in which all subcarriers of a channel overlap. IEEE 802.16e defines a zone of a frame to include a number of contiguous OFDMA symbols in an uplink (UL) or downlink (DL) that use the same operation mode. A DL or UL sub-frame may include one or more zones and may switch between the PUSC and FUSC operation modes between zones. In the PUSC operation mode, neighboring base stations (BSs) may be assigned to different segments to reduce interference between the neighboring BSs. In the FUSC operation mode, all BSs are assigned to use the entire channel.
Following the MBS approach, when broadcast services are to be provided in conjunction with cellular services, the broadcast services are provided within a zone (that may employ the PUSC operation mode) of a DL frame. In a cellular network that implements the MBS approach, within the zone, each BS transmits exactly the same broadcast information at exactly the same time, which requires time synchronization of all BSs. Theoretically, because all the BSs are fully synchronized and the broadcast information being transmitted by each of the BSs is identical (i.e., the information and encryption technique are the same), the transmitted signals add constructively, instead of interfering with each other, at a subscriber station. However, the broadcast capacity of MBS is limited by a framing time allocated for the broadcast service. Moreover, implementing MBS and cellular services on the same channel decreases an overall capacity of the channel to provide cellular services, due to the implementation of the broadcast services on the same channel. Furthermore, in cellular networks that employ cells operating at different frequencies, MBS is usually impractical due to limited data rates.
With reference to FIG. 2, a diagram 200 depicts example channel allocation and frame formats for two bases stations (BSs), i.e., BS1 (channel 204) and BS2 (channel 202), that provide broadcast services in a cellular network according to the MBS approach. The base stations BS1 and BS2 both transmit identical broadcast information on the same frequency band (shown separately as channels 204 and 202, respectively) during a zone of a downlink (DL) portion of framing periods 210. As is depicted, during each of the framing periods 210, the base stations BS1 and BS2 transmit a DL having an appropriate DL map (DLmap), an appropriate uplink (UL) map (ULmap), appropriate cellular traffic (CT) and identical broadcast traffic, e.g., in the form of video information (Video 1, Video2 and Video3) in a zone of the DL. Each framing period 210 also includes a UL portion in which a subscriber station (SS) may transmit information to a BS in the cellular network. As is apparent from the diagram 200 of FIG. 2, implementing broadcast services within a cellular network utilizing the MBS approach reduces the bandwidth available for providing cellular traffic, because broadcast services and cellular traffic reside on the same channel.
What is needed is a technique for providing broadband services within a cellular network that does not reduce an available bandwidth of the network for providing cellular traffic. It would also be desirable for the technique to increase broadcast capacity and deployment flexibility.